The manufacture of glass plates generally involves the cutting and sorting glass plates out of a glass strip pulled up from the furnace while the glass strip travels on the line conveyor. In cutting glass plates out of the glass strip, a single-grade sorting system has heretofore been employed where only those glass plates which are above the aimed-at quality are sorted out, with the balance discarded.
The conventional single-grade sorting/cutting system, however, has a disadvantage of poor yields in manufacturing products having strict quality requirements. Glass plates for automotive windshields, for example, are required to be free of flaws, and of a high quality from the viewpoint of safety. In the manufacturing process of glass plates for automotive windshields, therefore, they are inspected for the presence/absence of flaws, and any glass plates in which flaws are found are discarded.